Speaking at a Tilda Rice Mill in Rainham, Essex, the trio repeated their statement from a joint article for the Mail on Sunday that Britain was being “held to ransom” by hardline Brexiteers.

They say a hard Brexit threatens jobs and living standards in the UK.

Mr Miliband, who now heads the New York-based International Rescue Committee aid agency, denied he was seeking to launch a new, centrist political movement when asked by the BBC Radio 4 Today programme.

“This is about calling for MPs of all parties to stand together,” he said.

“The truth is that Britain is being held to ransom by the demand for hard Brexit, for severing the links with the customs union and the single market that is at the heart of the debate going on at the moment.

“It think that it is significant that people should come together, frankly out of alarm at the prospects for the UK.

“The prospects of a hard Brexit are very high now and, what’s worse, the prospect of no deal is rising too.

“It does not need to be like this. It is very, very important that the country is not held to the kind of ransom that at the moment threatens living standards as well as the political influence of the UK in a very fundamental way.”

Mr Miliband warned that currently the government does not have a settled position on the kind of future relationship it wants with the EU.

He added: “The negotiation is not with Europe at the moment; the negotiation is in the Cabinet room. This isn’t funny.

“We are less than 120 days away from the final negotiation.”

Mr Miliband also criticised Jeremy Corbyn over Labour’s refusal to support a Lords amendment that would allow Britain to become part of the European Economic Area (EEA) after it leaves the UK.

Ms Morgan criticised the language used in the Brexit debate and revealed she had been the subject of an alleged death threat.

She said people who voiced concerns about the Brexit process were branded “a mutineer, a saboteur or a traitor”.

The trio’s speech came as the European Union warned Britain time was running out to seal a Brexit deal this autumn.

“We are concerned that there is no clear stance, no clear position from the British. The clock is ticking,” German EU minister Michael Roth said.

“We need now to be making substantial progress, but that is not happening. What is worrying us in particular is the Northern Ireland question where we expect a substantial accommodation from the British side.”